Move character-related functions from Font to Character.

Introduce a new class, Character to hold all the fun statics
that deal with various character/codepoint properties of text.

Also add FontPlaftormFeatures class that holds statics that
define features, supported by each platform.

R=ksakamoto@chromium.org,eae
BUG=319475

Review URL: https://codereview.chromium.org/134163008

git-svn-id: svn://svn.chromium.org/blink/trunk@166236 bbb929c8-8fbe-4397-9dbb-9b2b20218538